Method for coating low viscosity materials

ABSTRACT

A method for coating low viscosity materials onto a wafer to form a uniform film. After a wafer is rotated at a first rotation speed, coating solution is drizzled onto the wafer. The wafer is decelerated to a second rotation speed at a first deceleration rate to spread the coating solution. Next, the wafer is slowly decelerated to a third rotation speed at a second deceleration rate considerably lower than the first deceleration rate, so the coating solution reflows to the center of the wafer. The wafer is then quickly accelerated to a fourth rotation speed at a third acceleration rate larger than the first deceleration rate to spread the coating solution again.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to manufacturingprocesses for semiconductor integrated circuit devices. Moreparticularly, to an improved method of applying a lower viscositycoating liquid, such as a photoresist solution and an anti-reflectionfilm coating (ARC) solution, onto a semiconductor wafer to form filmwith uniform surface.

[0003] 2. Description of the Related Art

[0004] Recently, wafer size tends to increase as device circuits areminiaturized. With this tendency, a low-viscosity photoresist solutionand low-viscosity anti-reflection coating film solution (hereinafterreferred to as “ARC solution”) have been increasingly used. For forminga thicker film coating the low-viscosity solution onto the wafer, thecommon method reduces the rotation speed of the wafer to increasecoating thickness. However, the thickness of the coating film is thickerthan the predetermined thickness and the uniformity is worse.

[0005] In general, the traditional coating process substantiallycomprises five steps.

[0006] Step I: spraying a solvent (also called prewetting)

[0007] Step II: drying the solvent

[0008] Step III: dispersing a coating solution

[0009] Step IV: spreading the coating solution

[0010] Step V: cleaning the wafer

[0011] An example using the traditional coating method to form aphotoresist film with predetermined thickness of 1350 Å is given inTable 1 and FIG. 1 which shows the wafer rotation speeds in each step.TABLE 1 Rotation Acceleration/ Time speed deceleration rate step (sec)(rpm) (rpm/sec) 1.0 0 I 1.5 0 Spraying a solvent II 3.0 2000 10000 III2.6 1000 10000 Dispersing a photoresist solution (2.5 cc/2.2 sec) IV95.0 525 10000 Spreading the photoresist solution V 1.0 2000 10000Cleaning edge of the wafer 5.0 2000 Cleaning edge/backside of the wafer1.0 2500 10000 Cleaning edge of the wafer 5.0 3000 10000 Cleaning edgeof the wafer 1.0 0 10000

[0012] Referring to Table 1 and FIG. 1, after the wafer is positioned ina spin coater and the rotation speed is kept at 0 rpm/sec, solvent issprayed on the surface of the wafer for 1.5 seconds to prewet thesurface of the wafer.

[0013] The solvent is dried while the wafer is accelerated from 0 rpm to2,000 rpm and kept at 2,000 rpm at a rate of 10,000 rpm/sec for 3seconds.

[0014] The photoresist solution is dispersed on the surface of the waferat a rate of 2.5 cc/2.2 sec for 2.6 seconds while the wafer isdecelerated from 2,000 rpm to 1,000 rpm at a rate of 10,000 rpm/sec.

[0015] The coating solution dispersed on the wafer is spread for 95seconds while the wafer is decelerated from 1,000 rpm to 525 rpm at arate of 10,000 rpm/sec to form the photoresist film with predeterminedthickness.

[0016] The wafer is accelerated from 1,000 rpm to 2,000 rpm at a rate of10,000 rpm/sec and kept at 2,000 rpm total for 1 second while the edgeof the wafer is cleaned. The wafer is kept at 2,000 rpm for 5 secondsand the edge and backside of the wafer are cleaned. The wafer isaccelerated from 2,000 rpm to 2,500 rpm at a rate of 10,000 rpm/secwhile the edge of the wafer is cleaned for 1 second. The wafer isaccelerated from 2,500 rpm to 3,000 rpm at a rate of 10,000 rpm/secwhile the edge of the wafer is cleaned for 5 seconds.

[0017] However, while the traditional coating method is used to form thephotoresist film in 8 inch wafers, the obtained photoresist film haspoor uniformity. As shown in FIG. 2, the average thickness of thephotoresist layer is 1331.19 Å, and the thickness variation is as highas 31.07 Å. In this manner, some problems may occur in subsequentprocesses such as photolithography and etching. For example, the widthof the conducting line formed after etching is not uniform, and yield isdecreased. These problems will become more serious with increases in thesize of the wafer.

SUMMARY OF THE INVENTION

[0018] The object of the present invention is to provide a method forcoating low viscosity materials to form a film with good uniformity.

[0019] To achieve the above-mentioned object, the present inventionprovides a method for coating low viscosity materials. After a wafer isrotated at a first rotation speed, coating solution is drizzled onto thewafer. The wafer is decelerated to a second rotation speed at a firstdeceleration rate to spread the coating solution. Next, the wafer isslowly decelerated to a third rotation speed at a second decelerationrate which is considerably lower than the first deceleration rate so thecoating solution reflows to the center of the wafer. The wafer is thenquickly accelerated to a fourth rotation speed at a third accelerationrate which larger than the first deceleration rate to spread the coatingsolution again.

[0020] In the above-mentioned method, the coating solution can be aphotoresist solution or an anti-reflection film coating (ARC) solution.The first deceleration rate, the second deceleration rate and the thirdacceleration rate are, for example, 10,000 rpm/sec, 100 rpm/sec and50,000 rpm/sec, respectively.

[0021] The present invention also provides another method for coatinglow viscosity materials comprising:

[0022] (a) spraying a solvent on a surface of a wafer;

[0023] (b) drying the wafer;

[0024] (c) dispersing a coating solution with a dispersing rate on thesurface of the wafer;

[0025] (d) first spreading the coating solution;

[0026] (e) reflowing the coating solution to the center of the wafer;and

[0027] (f) again spreading the coating solution.

[0028] In the above-mentioned steps, the dispersing rate of the coatingsolution is between 2.5 cc/2.2 sec and 1.5 cc/1.7 sec.

[0029] In the above-mentioned steps, the coating solution is aphotoresist solution or an ARC solution.

[0030] In the above-mentioned step (d), the method of first spreadingthe coating solution comprises decelerating the wafer from a firstrotation speed to a second rotation speed at a first deceleration rateand maintaining the wafer at the second rotation speed for a period oftime.

[0031] In the above-mentioned step (e), the method of reflowing thecoating solution to the center of the wafer comprises slowlydecelerating the wafer to a third rotation speed at a seconddeceleration rate, wherein the second deceleration rate is considerablylower than the first deceleration rate; and maintaining the wafer at thethird rotation speed for a period of time.

[0032] In the above-mentioned step (f), the method of again spreadingthe coating solution comprises quickly accelerating the wafer to afourth rotation speed at a third acceleration rate, wherein the thirdacceleration rate is higher than the first deceleration rate, andmaintaining the wafer at the fourth rotation speed for a period of time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawings,given by way of illustration only and thus not intended to be limitativeof the present invention.

[0034]FIG. 1 shows the wafer rotation speeds in each step for thetraditional coating method;

[0035]FIG. 2 is a graph showing the relation of the thickness of thephotoresist layer with positions on the wafer in accordance with thetraditional coating method;

[0036]FIG. 3 shows the wafer rotation speeds in each step in accordancewith the first embodiment of the present invention;

[0037]FIG. 4 is a graph showing the relation of the thickness of thephotoresist layer with positions on the wafer in accordance with thefirst embodiment of the present invention;

[0038]FIG. 5 is a graph showing the relation of the thickness of thephotoresist layer with positions on the wafer in accordance with thesecond embodiment of the present invention;

[0039]FIG. 6 shows the wafer rotation speeds in each step in accordancewith the third embodiment of the present invention; and

[0040]FIG. 7 is a graph showing the relation of the thickness of thephotoresist layer with positions on the wafer in accordance with thethird embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0041] In the traditional coating process, after dispersing the coatingsolution onto the wafer, the rotation speed of the wafer is reduced to adetermined speed and the coating solution is spread at the same time.Research has shown that poor coating film uniformity occurs when coatingsolution is spread only one time in the coating process.

[0042] In order to solve the above-mentioned problem, the presentinvention improves the step of spreading the coating solution.

[0043] The coating method provided in the present invention comprises:

[0044] Step I: spraying a solvent (also called prewetting)

[0045] Step II: drying the solvent

[0046] Step III: dispersing a coating solution

[0047] Step IV: spreading the coating solution, reflowing the coatingsolution to the center of the wafer, and respreading the coatingsolution

[0048] Step V: cleaning the wafer

[0049] After dispersing the coating solution on the surface of thewafer, the coating solution is spread twice, thereby providing moreuniform coating film. The coating solution can spread more than twice,and the present invention accordingly does not limit the process to twospreadings.

[0050] The coating method of the present invention will be explained indetail in the following embodiments.

[0051] First Embodiment

[0052] The coating method of the present invention coats a photoresistsolution to form a photoresist film with a thickness of 1350 Å. Adetailed coating recipe is given in Table 2. FIG. 3 shows the waferrotation speeds in each step according to the first embodiment of thepresent invention. TABLE 2 Rotation Acceleration/ time speeddeceleration rate step (sec) (rpm) (rpm/sec) 1.0 0 I 1.5 0 Spraying asolvent II 3.0 2000 10000 III 2.6 1000 10000 Dispersing a photoresistsolution (2.5 cc/2.2 sec) IV 30.0 525 10000 Spreading the photoresistsolution 50.0 50 100 Re-flowing the photoresist solution to the center15.0 521 50000 Re-spreading the photoresist solution V 6.0 2000 10000Cleaning edge and backside of the wafer 1.0 2500 10000 Cleaning edge andbackside of the wafer 5.0 3000 10000 1.0 0 10000

[0053] Step I

[0054] Referring to Table 2 and FIG. 3, after the wafer is positioned ina spin coater and the rotation speed of the wafer is kept at 0 rpm/sec,a solvent is sprayed on the surface of the wafer for 1.5 seconds toprewet the surface of the wafer.

[0055] Step II

[0056] The solvent is dried for 3 seconds while the wafer is acceleratedfrom 0 rpm to 2,000 rpm at a rate of 10,000 rpm/sec.

[0057] Step III

[0058] The photoresist solution is dispersed on the surface of the waferat a rate of 2.5 cc/2.2 sec for 2.6 seconds while the wafer isdecelerated from 2,000 rpm to 1,000 rpm at a rate of 10,000 rpm/sec.

[0059] Step IV

[0060] The coating solution dispersed on the wafer is spread for 30seconds a first time while the wafer is decelerated from 1,000 rpm to525 rpm at a rate of 10,000 rpm/sec, as shown in FIG. 3 marked A.

[0061] The wafer is then slowly decelerated from 525 rpm to 50 rpm at arate of 100 rpm/sec and kept at 50 rpm totally for 50 seconds, as shownin FIG. 3 marked R. In such manner, it takes 4.75 seconds to slowlyreduce the rotation speed from 525 rpm to 50 rpm so that the photoresistsolution can smoothly reflow from the edge to the center of the wafer.

[0062] The wafer is then quickly accelerated from 50 rpm to 521 rpm at arate of 50,000 rpm/sec and kept at 521 rpm totally for 15 seconds. Insuch manner, the photoresist solution is spread a second time, as shownin FIG. 3 marked B.

[0063] Step V

[0064] The wafer is accelerated from 1,000 rpm to 2,000 rpm at a rate of10,000 rpm/sec and kept at 2,000 rpm while the edge and backside of thewafer are cleaned for 6 seconds. The wafer is accelerated from 2,000 rpmto 2,500 rpm at a rate of 10,000 rpm/sec and the edge and backside ofthe wafer are cleaned for 1 second.

[0065] The wafer is accelerated from 2,500 rpm to 3,000 rpm at a rate of10,000 rpm/sec for 5 seconds.

[0066] The coating method of the first embodiment is used to uniformlycoat the photoresist film on the 8 inch wafer. The obtained photoresistfilm has good uniformity, as shown in FIG. 4. The average thickness ofthe photoresist layer is 1334.06 Å and the thickness variation isreduced to 14.46 Å.

[0067] Second Embodiment

[0068] In general, reducing the dispersing rate of the coating solutionreduces the loss of coating solution, thereby reducing production costs.However, the uniformity of the coating film is affected by reducing thedispersing rate of the coating solution. The lower the dispersing rate,the poorer the uniformity of the coating film.

[0069] However, in this embodiment the dispersing rate of thephotoresist solution is reduced from 2.5 cc/2.2 sec used in step III inthe first embodiment to 1.5 cc/1.7 sec.

[0070] Using the above-mentioned coating method on an 8 inch wafer, aphotoresist film with good uniformity is obtained. As shown in FIG. 5,the average thickness of the photoresist film is 1340.00 Å, and thethickness variation is 15.63 Å. Although the thickness variation underthe recipe in this second embodiment is slightly higher than that in thefirst embodiment, the coating film formed with the recipe in this secondembodiment still exhibits good uniformity.

[0071] Therefore, for the coating method of the present invention, theamount of the coating solution can be reduced without affecting theuniformity of the coating film, thereby reducing production costs.

[0072] Third Embodiment

[0073] The time spent in step IV in the first embodiment is 95 seconds,and step IV takes more time than the other steps of the whole coatingprocess. Step IV is thus a bottleneck step for the whole coatingprocess.

[0074] In this embodiment, the time spent in step IV is reduced from 95seconds in the first embodiment to 65 seconds. A detailed coating recipeis given in Table 3. FIG. 6 shows the wafer rotation speeds in eachstep. TABLE 3 Rotation Acceleration/ time speed deceleration rate step(sec) (rpm) (rpm/sec) 1.0 0 I 1.5 0 Spraying a solvent II 3.0 2000 10000III 2.6 1100 10000 Dispersing a photoresist solution (1.5 cc/1.7 sec) IV30.0 472 10000 Spreading the photoresist solution 20.0 50 100 Re-flowingthe photoresist solution to the center 15.0 521 50000 Re-spreading thephotoresist solution V 6.0 2000 10000 Cleaning edge and backside of thewafer 1.0 2500 10000 Cleaning edge and backside of the wafer 5.0 300010000 1.0 0 10000

[0075] Step I

[0076] Referring to Table 3 and FIG. 6, after the wafer is positioned ina spin coater and the rotation speed of the wafer is kept at 0 rpm/sec,a solvent is sprayed on the surface of the wafer for 1.5 seconds toprewet the surface of the wafer.

[0077] Step II

[0078] The solvent is dried for 3 seconds while the wafer is acceleratedfrom 0 rpm to 2,000 rpm at a rate of 10,000 rpm/sec.

[0079] Step III

[0080] The photoresist solution is dispersed on the surface of the waferat a rate of 1.5 cc/1.7 sec for 2.6 seconds while the wafer isdecelerated from 2,000 rpm to 1,100 rpm at a rate of 10,000 rpm/sec.

[0081] Step IV

[0082] The coating solution dispersed on the wafer is spread for 30seconds a first time while the wafer is decelerated from 1,100 rpm to472 rpm at a rate of 10,000 rpm/sec, as shown in FIG. 6 marked A.

[0083] The wafer is then slowly decelerated from 472 rpm to 50 rpm at arate of 100 rpm/sec and kept at 50 rpm totally for 20 seconds, as shownin FIG. 6 marked R. In such manner, it takes 4.22 seconds to slowlyreduce the rotation speed from 472 rpm to 50 rpm so that the photoresistsolution can smoothly reflow from the edge to the center of the wafer.

[0084] The wafer is then quickly accelerated from 50 rpm to 521 rpm at arate of 50,000 rpm/sec and kept at 521 rpm totally for 15 seconds. Insuch manner, the photoresist solution is spread a second time, as shownin FIG. 6 marked B.

[0085] Step V

[0086] The wafer is accelerated from 1,000 rpm to 2,000 rpm at a rate of10,000 rpm/sec and kept at 2,000 rpm while the edge and backside of thewafer are cleaned for 6 seconds. The wafer is accelerated from 2,000 rpmto 2,500 rpm at a rate of 10,000 rpm/sec and the edge and backside ofthe wafer are cleaned for 1 second.

[0087] The wafer is accelerated from 2,500 rpm to 3,000 rpm at a rate of10,000 rpm/sec for 5 seconds.

[0088] The coating method of the third embodiment is used to coat thephotoresist film with a uniformity thickness on the 8 inch wafer. Theobtained photoresist film has good uniformity, as shown in FIG. 4. Theaverage thickness of the photoresist layer is 1305.33 Å and thethickness variation is reduced to 13.72 Å.

[0089] Therefore, the time spent in step IV can be reduced using thecoating method of the present invention. The time spent in step IV cansave 30 seconds or more without affecting the uniformity of the coatingfilm, thereby improving the production yield.

[0090] As mentioned above, a photoresist film or an ARC film with gooduniformity can be obtained using the coating method of the presentinvention. Furthermore, the dispersing rate of the coating solution canbe reduced to decrease the amount of the coating solution, therebyreducing production costs. Moreover, the total time spent to spread thecoating solution (that is the bottleneck step, step IV) can be reducedto improve the production yield.

[0091] The foregoing description of the preferred embodiments of thisinvention has been presented for purposes of illustration anddescription. Obvious modifications or variations are possible in lightof the above teaching. The embodiments were chosen and described toprovide the best illustration of the principles of this invention andits practical application to thereby enable those skilled in the art toutilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. All suchmodifications and variations are within the scope of the presentinvention as determined by the appended claims when interpreted inaccordance with the breadth to which they are fairly, legally, andequitably entitled.

What is claimed is:
 1. A method for coating low viscosity materials,comprising: providing a wafer, wherein the wafer is rotated at a firstrotation speed; drizzling a coating solution onto the wafer;decelerating the wafer to a second rotation speed at a firstdeceleration rate to spread the coating solution; and slowlydecelerating the wafer to a third rotation speed at a seconddeceleration rate, wherein the second deceleration rate is considerablylower than the first deceleration rate so the coating solution reflowsto the center of the wafer; and quickly accelerating the wafer to afourth rotation speed at a third acceleration rate, wherein the thirdacceleration rate is higher than the first deceleration rate, therebyspreading the coating solution again.
 2. The method as claimed in claim1, wherein the coating solution is a photoresist solution.
 3. The methodas claimed in claim 1, wherein the coating solution is an ARC solution.4. The method as claimed in claim 1, further comprising, beforedrizzling the coating solution onto the wafer, prewetting a surface ofthe wafer with a solvent and drying.
 5. The method as claimed in claim1, further comprising, after spreading the coating solution again,cleaning the wafer.
 6. The method as claimed in claim 1, wherein thefirst deceleration rate is 10,000 rpm/sec, the second deceleration rateis 100 rpm/sec, and the third acceleration rate is 50,000 rpm/sec.
 7. Amethod for coating low viscosity materials, comprising: (a) spraying asolvent on a surface of a wafer; (b) drying the wafer; (c) dispersing acoating solution on the surface of the wafer; (d) spreading the coatingsolution; (e) reflowing the coating solution to the center of the wafer;and (f) again spreading the coating solution.
 8. The method as claimedin claim 7, wherein the coating solution is a photoresist solution. 9.The method as claimed in claim 7, wherein the coating solution is an ARCsolution.
 10. The method as claimed in claim 7, wherein in the step (d),the method of first spreading the coating solution comprises:decelerating the wafer from a first rotation speed to a second rotationspeed at a first deceleration rate; and maintaining the wafer at thesecond rotation speed for a period of time.
 11. The method as claimed inclaim 10, wherein in the step (e), the method of reflowing the coatingsolution to the center of the wafer comprises: slowly decelerating thewafer to a third rotation speed at a second deceleration rate, whereinthe second deceleration rate is considerably lower than the firstdeceleration rate; and maintaining the wafer at the third rotation speedfor a period of time.
 12. The method as claimed in claim 11, wherein inthe step (f), the method of again spreading the coating solutioncomprises: quickly accelerating the wafer to a fourth rotation speed ata third acceleration rate, wherein the third acceleration rate is higherthan the first deceleration rate; and maintaining the wafer at thefourth rotation speed for a period of time.
 13. The method as claimed inclaim 7, further comprising, after again spreading the coating solution,cleaning the wafer.
 14. The method as claimed in claim 7, wherein thecoating solution is dispersed at a dispersing rate between 2.5 cc/2.2sec and 1.5 cc/1.7 sec.